Electrically heated compressor blade



y 1956 H. s. RAINBOW 2,754,398

ELECTRICALLY HEATED COMPRESSOR BLADE med Dec. 12, 1952 2 Sheets-Sheet 1l 5. Fan/50W July 10, 1956 H. s. RAINBOW ELECTRICALLY HEATED COMPRESSORBLADE 2 Sheets-Sheet 2 Filed Dec. 12, 1952 United States PatentELECTRICALLY HEATED COMPRESSOR BLADE Horace Sinclair Rainbow, Coventry,England, assignor lto Armstrong Siddeley Motors Limited, Coventry, Eng

and

Application December 12, 1952, Serial No. 325,527

Claims priority, application Great Britain December 17, 1951 Claims.(Cl. 219-19) The main object of this invention is the protection ofaerofoil bodies, disposed in a duct through which an airstream passes,against ice formation thereon, for example, the protection of the inletguide blades and the early rows of blades of an axial-flow compressor.

The invention is particularly concerned with a method of electricallyheating such areofoil bodies.

According to the invention, such an aerofoil body is formed hollow andprovided with an internal electrical heating element which is insulatedtherefrom, the hollow body being filled with an electrically insulatingfluid with good heat transmitting properties, and the element havingconnections to an electrical circuit through means closing the ends ofthe hollow body.

In this way the electrical heating element (which can be chosen toproduce any desired degree of heating) heats the fluid within the hollowbody, and the latter itself becomes heated by conduction or convection,or by a combination of the two.

In the accompanying drawings:

Figure l is a sectional elevation showing one construction of inletguide blade for an axial-flow compressor, according to the invention,with certain parts of the compressor omitted for the sake of clearness;

Figure 2 is a more detailed sectional elevation, and to a larger scale,of a preferred construction according to the invention;

Figure 3 is a transverse sectional elevation taken mainly on the line3-3 of Figure 2;

Figure 4 is a cross-section taken on the line 44 of Figure 3;

Figure 5 is a fragmentary perspective view, to a still larger scale,showing part of the heating element and the associated insulatingsupport in the interior of the blade; and

Figure 6 is a perspective view of an insulating support at the lower endof the heating element.

In the construction of Figure 1, the hollow blade 11 (representative ofany blade in the row) is closed at the ends by plates 12, 13 which aresecured thereto in any suitable manner, and each of these plates, rounda central opening, is fast with a tubular extension 14, 15 forming themounting at that end. As more fully described with reference to Figures2 to 6, the tubular extension 14 at one end of the blade can be squareand coact with a hole of the same cross-section in one of the supportingrings (not shown), whereby to locate the blade in its proper angularposition but in a manner to accommodate expansion movements of the bladein the radial direction of the supporting ring. The other extension 15is of circular cross-section for engagement in a circular hole of theother supporting ring, this extension being provided at opposite endswith lateral flanges 17, 18 affording radial location of the blade inthe associated ring. The latter, for that purpose, can be formed of twoside-by-side ring parts with the division extending axially through allthe holes (as shown in Figure 2) Within the tubular extensions at bothends of the blade is a connection 20 for an electrical heating element21, which latter is supported, with clearance, within the blade, theconnections being insulated from the extensions by insulators 22, 22.Each of these elements may be in the form of a wire in which case theends of the Wire can extend into and be attached to the connections 20as shown in Figure 1, the connections extending with clearance throughthe central openings aforesaid. Each connection, axially beyond the endsof the tubular extensions, is fast with terminals 23 or 24 by which theheating elements of adjacent blades can be connected, as desired, in anelectrical circuit. These terminals are insulated from the extensions byflanges on the insulators, as indicated at 26, 27.

Preferably the fluid, with which the blade is filled at any appropriatetime during its manufacture through one of the central openings in oneof the end plates, is a liquid such as an oil of the kind commonly usedfor cooling electrical transformers. The engagement between theinsulators and connections and extensions is such as to prevent escapeof the liquid.

In the construction of Figures 2 to 6, the main differences from that ofFigure 1 are that the heating element 21a in the interior of a blade 11ais of tortuous shape, and that the two ends of the heating element arefast with connecions 20a which extend through one of the tubularextensions 14a and are secured to terminals 28 by which the heatingelements of adjacent blades can be connected, as desired, in anelectrical circuit.

In Figures 2 and 3 the tubular extension 140, fast with the end plate12a closing the adjacent end of the blade, is of rectangular section,whilst the tubular extension 15a, fast with the other closing end plate13a, has flanges 17a, 1811 providing radial location in a supportingring. This supporting ring is built up of two separate portions 30, 31which are secured to one another as by studs and nuts 32, the divisionbeing through the holes 33 (for the extensions 15a) provided jointly bythe two portions. The tubular extension 15a has a filling passage 35provided in it, this passage being closed by means of a soft plug 36held in position by a hard plug 37 which, in "its turn, is located bythe metal of the tubular extension being peened over it, as shown at 38in Figure 2.

On the other hand, the tubular extension 14a is a sliding fit in acorresponding hole of rectangular section provided in a ring 39 which issupported in any convenient manner by a structural member 40 of thecompressor. A clearance to allow for radial expansion is shown at 41.The connectors 20a to the ends of the heating element pass throughinsulating bushes 42, 42 located in the end plate 12a and its associatedextension 14a, and also through an insulating washer 43 below the endplate 12a. The free interior of the tubular extension, round theterminals 28, is filled with an insulating resin 44.

It will be seen that the heating element is substantially symmetricalabout the line 3-3 in Figure 2, being supported at its lower end, andhaving its two halves 45, 46 held separated from one another, by aninsulating member 47. This member has legs 48 which rest upon theadjacent end plate 13a, and end faces 49, 49 which engage the adjacentinternal surfaces of the blade. A clearance is shown at 50 to allow forexpansion of the heating element when starting up.

In addition, each of the halves 45, 46 of the heating element is formedas an open loop having between its two limbs an insulating strip 51.Each of these strips, at intervals along its length, has integrallyformed side faces 53, 53 which engage the adjacent internal faces of theblade, and two slit supports 54, 54 which receive the respective runs ofthe associated half of the heating element.

In this way the heating element is firmly supported against contact withthe interior of the blade, and it offers a substantial heating areawhereby to heat the liquid enclosed in the interior of the blade.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

1. An axial flow compressor blade comprising means for protectingagainst ice formation thereon, said blade being open-ended, hollow, ofaerofoil cross-section, and said means including plates secured to andclosing the ends of the blade, said plates carrying mounting means forthe blade, electric terminals extending through and insulated from saidmounting means and extending from the exterior to the interior of saidblade, an electric heating element spaced interiorly from the walls ofsaid blade and interconnecting said terminals whereby said element willbe heated when said terminals are connected in an electric circuit, andan insulating liquid having good heattransferring propertiessubstantially filling the rest of the interior of said blade.

2. A hollow, open-ended axial compressor blade of aerofoil cross-sectioncomprising means secured to and closing the open ends of said blade,electric terminals extending from the exterior to the interior of saidblade, said terminals insulated from said blade and for incorporationinto an electrical circuit, an electrical heating element in said bladeextending between and secured to said terminals, said heating elementextending substantially throughout the length of the interior of saidblade, and an electrically insulating and heat-transmitting fluid insaid blade in contact with the interior walls thereof and with saidheating element.

3. A hollow, open-ended blade of aerofoil cross-section and for use inan axial flow compressor, means secured to and closing the open ends ofsaid blade, electric terminals extending from the exterior to theinterior of said blade, said terminals insulated from said blade and forincorporation into an electrical circuit, an electrical heating elementin said blade extending between and secured to said terminals, and anelectrically insulating and heat transmitting liquid in said blade incontact with the interior walls thereof and with the heating element, inwhich said heating element is of tortuous form and rigid insulatingmeans are included between the heating element and the wall of theblade.

4. A hollow, open-ended blade of aerofoil cross-section and for use inan axial flow compressor, means secured to and closing the open ends ofsaid blade, electric terminals extending from the exterior to theinterior of said blade, said terminals insulated from said blade and forincorporation into an electrical circuit, an electrical heating elementin said blade extending between and secured to said terminals, and anelectrically insulating and heat transmitting liquid in said blade incontact with the interiorwalls thereof and with the heating element, inwhich said heating element is of tortuous form and rigid insulatingmeans are included between the heating element and the wall of theblade, and in which said heating element comprises two generally similaropen loops connected to one another.

5. A hollow, open-ended blade of aerofoil cross-section and for use inan axial flow compressor, means secured to and closing the open ends ofsaid blade, electric terminals extending from the exterior to theinterior of said blade, said terminals insulated from said blade and forincorporation intoan electrical circuit, an electrical heating elementin said blade extending between and secured to said terminals, and anelectrically insulating and heat 7 References Cited-in ,the'file of thispatent UNITED STATES PATENTS 664,776 Porter Dec. 25, 1900 1,705,126 LeeMar.'12,1929 1,750,777 Ingram Mar. 18, 1930 2,269,566 Van Daam Ian. 13,1942 2,402,770 Poekel June 25, 1946 2,418,205 Taylor Apr. 1, 19472,591,757 Young Apr. 8, 1952

